A 1 file is a manual page (or "man page") used by Man utility, a Unix program used to view user manuals. It contains level 1 user manuals stored in plain text and separated into several segments and delimited by standard markers.

Level 1 user manuals describe general commands for the Unix operating system. They are stored in files that contain the name of the command followed by the ".1" extension. For example, a manual for the command "cmd_example" would have the filename "cmd_example.1." Since Unix man pages are stored in a plain text format, they can be created and edited with any text editor. NOTE: Unix man page files are commonly compressed into .GZ files and have the ".gz.1" compound extension. Unix man pages also use the ".2" through ".8" extensions for other sections. For example, the ".2" extension is used for System Calls documentation.